Term for when people lack the experience or knowledge to understand a metaphor?

First of all I would like to say that I`m not a native speaker, but I think that ''non-cognitive'' is the term you are looking for !

If you are trying to remember something you have read in the context of metaphors that fall flat, maybe that was the expression "dead metaphor". When everyone saw horses every day, the metaphor "he took the bit between his teeth" made sense, but does it now? It is dead (or on the way there).

"Other people can't understand since they did not make all the thought gymnastics to have that view point."

I believe you're thinking of something along the lines of an individual's mental model.

From Wikipedia:

A mental model is an explanation of someone's thought process about how something works in the real world. It is a representation of the surrounding world, the relationships between its various parts and a person's intuitive perception about his or her own acts and their consequences. Mental models can help shape behaviour and set an approach to solving problems (similar to a personal algorithm) and doing tasks.

A mental model is a kind of internal symbol or representation of external reality, hypothesized to play a major role in cognition, reasoning and decision-making. Kenneth Craik suggested in 1943 that the mind constructs "small-scale models" of reality that it uses to anticipate events.

Jay Wright Forrester defined general mental models as:

The image of the world around us, which we carry in our head, is just a model. Nobody in his head imagines all the world, government or country. He has only selected concepts, and relationships between them, and uses those to represent the real system (Forrester, 1971).

In psychology, the term mental models is sometimes used to refer to mental representations or mental simulation generally. At other times it is used to refer to § Mental models and reasoning and to the mental model theory of reasoning developed by Philip Johnson-Laird and Ruth M.J. Byrne.

As each person has their own subjective experiences so does each person have their own mental model of the way the world works—and each person forms their own associations between things and events and outcomes. It's those parts of our mental models that we have in common that allow us to interact with each other. But we can also think and react uniquely because of the differences between our individual mental models.

So, when your person looks at a pot of boiling water, it triggers an association that they have (and which others don't) that leads them to think of a solution to a problem that others cannot.

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Returning to the original question of metaphors (although you've since indicated that wasn't your main point), if you don't understand the references behind a metaphor (they are not part of your mental model), then you will not be able to form the relationships required to understand the metaphor.

A “colloquialism” is a word or phrase based on informal conversation. It requires prior knowledge or experience to understand.